Abstract

We demonstrate a new approach to measuring high-order temporal coherences that uses a four-element superconducting nanowire single-photon detector. The four independent, interleaved single-photon-sensitive elements parse a single spatial mode of an optical beam over dimensions smaller than the minimum diffraction-limited spot size. Integrating this device with four-channel time-tagging electronics to generate multi-start, multi-stop histograms enables measurement of temporal coherences up to fourth order for a continuous range of all associated time delays. We observe high-order photon bunching from a chaotic, pseudo-thermal light source, measuring maximum third- and fourth-order coherence values of 5.87 ± 0.17 and 23.1 ± 1.8, respectively, in agreement with the theoretically predicted values of 3! = 6 and 4! = 24. Laser light, by contrast, is confirmed to have coherence values of approximately 1 for second, third and fourth orders at all time delays.

Figures (4)

Scanning-electron microscope image of the four-element SNSPD, with nanowire elements 0-3 traced out in color. Each element consists of a ~5 nm-thick × 80 nm-wide NbN nanowire on a sapphire substrate, with 60 nm gaps between wires. The 9.4 µm-diameter active area is well matched to the spatial mode of a single mode optical fiber, the cleaved end of which is held within ~10 µm of the detector surface. The interleaved design ensures that all four elements equally sample this spatial mode.

(a) Measured third-order coherence from the chaotic source, where both color and height indicate measured value of g(3). The cross-section in Fig. 2(a) samples these data along a diagonal line (not shown) extending from the far left corner to the far right corner as plotted here. (b) Calculated third-order coherence for a chaotic source derived from an ideal Gaussian scattering process with a coherence time of 900 ns, as discussed in the text.